Templates now no longer use Make variables for substitution
but instead replace strings with their equivalent:

  template_name: Corresponds to n=template_name
  project_name:  Corresponds to $(PROJECT) or in=project_name

This allows defining templates outside of Makefiles. For
example an external plugin could define their templates
in templates/my_template.erl and then have the following
in the included Makefile:

  tpl_my_template = $(file < $(THIS)/templates/my_template.erl)

By default the created file will be in src/template_name.erl.
This can be overriden with the tplp_* variable:

  tplp_my_template = src/model/my_template.erl

Substitution is applied both to the template contents and
to its path.

In addition, attempting to overwrite an existing file when
creating a template will result in failure.

This includes the SSL security fix for OTP-25+.

We use $1 instead of $(1) or $p instead of $(p) when possible,
except when building variable names (pkg_$(p)_name for example,
but also $(dep_fetch_$(1))).

This method dates back from the beginnings of Erlang.mk
and should not have been used for around a decade by now.
Adding "git" to the offending dep lines is enough to upgrade.

Use the query_* equivalents instead.

This should both be more solid and more secure.